Speckle reducer using a beam-splitter

ABSTRACT

Assembly ( 1 ) comprising a laser source ( 3 ) and a component for reducing speckle ( 7 ) comprising a beam splitter ( 9 ) that reflects a first portion ( 11 ) of the laser beam and transmits a second portion ( 13 ) and a first and second reflecting means ( 15, 17 ), the first reflective means ( 15 ) receiving the second portion ( 13 ) of the laser beam and the second reflective means ( 17 ) directing said second portion ( 13 ) back to the beam splitter ( 9 ), wherein the second portion ( 13 ) of the laser beam can be directed from the first ( 15 ) to the the second reflective means ( 17 ), wherein the first ( 15 ), the second ( 17 ) reflective means and the means for beam splitting ( 9 ) define an optical path for the second portion ( 13 ) of the laser beam, the length of which being equal to, or greater than, the coherence length of the laser beam.

FIELD OF THE INVENTION

The present invention concerns a light assembly, and in particular, butnot exclusively, a light assembly which uses a block to provide anoptical path for a portion of a laser beam whose length is equal to, orgreater than, a coherence length of the laser beam, so as to reducespeckle.

DESCRIPTION OF RELATED ART

Speckle is a phenomenon created with light sources, e.g. laser lightsources, due to the fact that light is coherent. Parallels andsynchronized wavefronts simultaneously hit the projection surface. Whenthe light hits the surface, it creates constructive and destructiveinterference. The interferences induce an image deterioration that isoften visible by human eye and/or by sensors. In addition to a loss ofimage quality, visual comfort of the viewer may also be affected.

One of the most common ways to reduce speckle is to combine laser beamswhich have different speckle patterns. Typically this is achieved byoverlaying the beam spot (the Gaussian beam intensity distribution at agiven intensity) of one laser beam which has a speckle pattern with thebeam spots of other laser beams which have different uncorrelatedspeckle patterns to provide a single beam spot with reduced speckle.Combining the laser beams which have different speckle patterns resultsin an averaging of the speckle patterns which reduces visible speckleeffect.

Laser projection systems are particularly affected by the speckleeffect. The speckle effect causes a variation in the intensity withpixel of a projected image. This variation in intensity within eachpixel results in a deformed projected image with visual effect ofun-sharp edges.

In a projection system, a 2-D image or a video can be displayed on adisplay surface; each pixel of the 2-D image or a video is generated bycombining modulated red, green and blue and/or other wavelength laserlight sources, such as UV or IR, by means of, for example, a beamcombiner. The combined light from the modulated red, green and bluelaser is emitted from the beam combiner as a beam of light. The beam oflight emitted from the beam combiner comprises pulses, and each pulsewill correspond to a pixel of the 2-D image or a video. One or more MEMSmicro-mirrors are used to direct the beam of light to a display screen;the one or more MEMS micro-mirrors will oscillate to scan the beam oflight in a zig-zag, unidirectional or bidirectional raster (interlacedor not interlaced) or lissajou pattern across the display screen so thatthe 2-D image, or a video, is displayed on the display screen,pixel-by-pixel. The MEMS micro-mirror(s) will continuously oscillate toscan light, for example, from left to right and from top to bottom sothat each pixel of the 2-D image or a video which is projected onto thedisplay surface, is continuously refreshed. The speed of oscillation ofthe MEMS micro-mirror is such that a complete 2-D image or a video isvisible on the display surface.

For laser projection systems which scan light e.g. MEMS-laser projectionsystems, reducing speckle is difficult to achieve. This is becausespeckle occurs in each individual pixel and therefore the steps toreduce speckle must be carried out before the MEMS micro-mirror(s) hasoscillated to project the next pixel on the display screen. Since theMEMS micro-mirror must oscillate very fast (so that a complete 2-D imageor a video is visible on the display surface), the time period ofcarrying out steps to reduce speckle is very restricted.

A further challenge is that since such laser projection systemstypically use red, green and blue light sources, speckle reduction mustbe carried out on the laser beams provided by each of the red, green andblue light sources.

A further requirement is that the means for speckle reduction shouldhave little or no light loss. Loss of light will reduce the brightnessof the projected image.

Many steps have been taken to reduce the occurrence of speckle in laserprojection systems. One prominent method is that disclosed in US patentapplication US2012/0075588; in this particular patent application theprinciple is to split two orthogonal polarisations of a laser beam, andto pass direct each polarization along a different length paths;accordingly the two polarisations will provide two different specklepatterns The two different polarisations can each further split toprovide a total of four polarisations each with different specklepatterns

The contrast ratio provides a measure of speckle pattern. The contrastratio is given by the formula:

σ/I

Wherein ‘σ’ is the standard deviation and ‘I’ is the mean intensity ofthe optical light of the image. Speckle reduction is given by theformula:

1/√N

wherein ‘N’ is the number of different uncorrelated speckle patterns ofsame mean intensity.

Since the method of US2012/0075588 provides two different specklepatterns, the reduction in speckle which is indicated by a reduction ofa contrast ratio of 30% (1/√2). Such a reduction is insufficient formany applications.

Furthermore, the device disclosed in US2012/0075588 uses quarter-waveplates which are required to change the polarity of the laser beams thatpass through them; these quarter-wave plates are very expensive,increase the cost of the device, as well as inducing a lot of opticallosses.

It is an aim of the present invention to mitigate or obviate at leastsome of the above-mentioned disadvantages.

BRIEF SUMMARY OF THE INVENTION

According to the invention there is provided a light assemblycomprising, at least one laser source which is operable to emit a laserbeam, and a component for reducing speckle, wherein the component forreducing speckle is arranged to receive the laser beam, wherein thecomponent for reducing speckle comprises, a means for beam splittingwhich is configured to split the laser beam emitted by the laser, byreflecting a first portion of the laser beam and transmitting a secondportion of the laser beam; and at least a first and second reflectivemeans, wherein the first reflective means is arranged to receive thesecond portion of the laser beam from the means for beam splitting andthe second reflective means is arranged such that it can direct thesecond portion of the laser beam back to the means for beam splittingand wherein the first and second reflective means are arranged such thatthe second portion of the laser beam can be directed from the firstreflective means to the second reflective means; and wherein the atleast first and second reflective means and means for beam splitting arearranged to define an optical path for the second portion of the laserbeam whose length is equal to, or greater than, a coherence length ofthe laser beam which is emitted from the at least one laser source.

The component for reducing speckle comprises first and second mirrorwhich define the first and second reflective means, wherein the firstand second mirrors and a beam splitter plate, wherein each of the firstmirror, second mirror and beam splitter plate are mechanicallyindependent of one another such that each of the first mirror, secondmirror and beam splitter plate can be moved independently of the oneanother.

The component for reducing speckle may comprise a block, comprising afirst part which has a first, second and third surface, and wherein eachof the first and second and third surfaces are in optical communicationwith the means for beam splitting; and wherein the first surface of theblock comprises the first reflective means, and wherein the secondsurface of the block comprises the second reflective means, and whereinthe third surface of the block comprises the means for beam splitting.

Coherence length of a light beam is the propagation distance from acoherent light source (i.e. laser light beam) to a point where thepropagated light wave is no longer equal (in term of phase orwavelength) to the initially emitted wave. Within this propagationdistance, the wave in questions is most similar to a perfect sinusoidalwave. The coherence length L_(c) is given by:

L _(c)=(2 ln(2)λ² /nΔλ)

where λ is the laser's wavelength, Δλ the spectral width of the sourceand n the refractive index of the medium.

The means for beam splitting may comprise a coating provided on thethird surface of the block. The means for beam splitting may be definedby a coating provided on the third surface of the block

The first surface of the first part may comprise a reflective coatingwhich defines the first reflective means and the second surface of thefirst part comprises a reflective coating which defines the secondreflective means.

The light assembly may further comprise a second part which comprises afourth, fifth and sixth surface, wherein the fourth surface of thesecond part and fifth surface of the second part are configured to be inoptical communication with the means for beam splitting such that alaser beam received by the fourth surface can be passed to the means forbeam splitting and laser beams reflected by, or emitted from, the meansfor beam splitting can be received by the fifth surface of the secondpart, wherein the fifth surface of the second part is configured to emitlaser beams which it receives from the means for beam splitting suchthat both the first portion of the laser beam which is reflected by themeans for beam splitting and at least a part of the second portion ofthe laser beam which has been transmitted through the means for beamsplitting to the first and second reflective means and back through themeans for beam splitting, can be emitted through from the block throughthe fifth surface of the second part.

The fourth and fifth surfaces of the second part of the block may eachcomprise an anti-reflective coating.

The sixth surface is preferably arranged to abut the third surface ofthe first part

It will be understood that the means for beam splitting mayalternatively comprise a coating provided on the sixth surface of thesecond part of the block. It will be understood that the means for beamsplitting may alternatively be defined by a coating provided on thesixth surface of the second part of the block and a coating provided onthe third surface of the first part of the block.

The first part of the block is preferably composed of glass. The secondpart of the block is preferably composed of glass.

The block may comprise glass, PMMA (Poly-methyl-methacrylate), Pyrex,zerodur, borofloat material, polymer, borosilicate crown, dense flint orplastic. The first part and/or second part of the block may compriseglass, PMMA (Poly-methyl-methacrylate), Pyrex, zerodur, borofloatmaterial, polymer, borosilicate crown, dense flint or plastic. The blockis preferably made of a material, which enables light to transmitthrough. It is thus preferred if the material has as less light loss aspossible in terms of transmission. Preferably the block comprises SF2 orBK7, which is under the category of glass. The first part and/or secondpart of the block may comprise SF2 or BK7, which is under the categoryof glass.

Preferably the first part and second part may cooperate to define asingle unit. Preferably the first part and second part cooperate byconnecting; i.e. the first part and second part are connected togetherto form a single unit.

The first and second parts may each be configured to have a triangularcross section or truncated-triangular cross section. Preferably thefirst and second parts are configured to have a triangular crosssection. The triangular cross section is preferably an equilateraltriangle. The triangular cross section maybe an isosceles triangle. Thepath followed by a laser beam directed from the means for beam splittingto the first reflective means, to the second reflective means, and backto the means for beam splitting should be triangular. Depending on theinput angle α of the light beam to the block according to the normal,the angle of reflection of the two reflective surfaces should be set tofulfil the equation: 180=2α+β+Ω where β is the angle defined between theinput light and reflected light on the first reflective surface and Ω isthe angle defined between the first reflected light and the reflectedlight on the second reflective surface. Preferably β=Ω corresponding toan optical path forming a isosceles triangle.

The block may be configured such that the first and second parts arechangeable; in this manner each of the first and second parts may beselectively exchanged with other first and second parts which havesurfaces orientated at different angles i.e. first and second partswhich have different dimensions. A user can thus select to use first andsecond parts which have the appropriate orientated surfaces (i.e.dimensions) which provides a desired direction of laser input and outputemission.

The first and second surfaces of the first part may be orientated suchat least part of the second portion of the laser beam which has beentransmitted, through the means for beam splitting to the first andsecond reflective means and back through the means for beam splitting,is emitted from the means for beam splitting in the same direction asthe direction in which the first portion of the laser beam is reflectedby the means for beam splitting, so that said least a part of the secondportion of the laser beam and the first portion of the laser beam areemitted from the block in the same direction or in parallel. The blockmay be shaped or configured such that first and second surfaces areorientated in this way.

The block may be configured, for example shaped, such that there is apredetermined angle between the first and second surfaces to provide apredetermined angle between the first and second reflecting means, sothat there is predetermined angle between a laser beam which is incidenton the block and a laser beam which is emitted from the block.

The first, second, fourth and fifth surfaces may be orientated such thatthe first portion of the laser beam and said at least a part of thesecond portion of the laser beam, can be emitted from the fifth surfaceof the second part of the block in the same direction and/or parallel.

The block may be configured such that there is a predetermined anglebetween the first and second surfaces and between the fourth and fifthsurfaces so that there is predetermined angle between a laser beam whichis incident on the fourth surface of the block and a laser beam which isemitted from the fifth surface of the block. Said first portion of thelaser beam and said at least a part of the second portion of the laserbeam are laser beams which are emitted from the fourth surface of theblock.

Preferably the first portion of the laser beam and said at least a partof the second portion of the laser beam, will be emitted from the fifthsurface of the block in the same direction and/or parallel, so therewill be a predetermined angle will exist between the light beam which isincident on the fourth surface of the block and each of, the firstportion of the laser beam and said at least a part of the second portionof the laser beam.

For example, the block may be configured so that there is apredetermined angle between the first and second surfaces of the blockin the first part, and between the fourth and fifth surfaces of theblock in the second part, so that light can be emitted from the block ata predetermined angle. The block may be configured to emit light at apredetermined angle for a given angle of incidence on the fourth surfaceof the block; in such cases the orientation of block relative to thelaser source is determined so that the surfaces can be orientated at theappropriate angle.

For example, the block may be shaped so that there is an angle of 60°between the first and second surfaces, and an angle of 120° between thefourth and fifth surfaces; in such a case, provided that a laser beam isincident on the fourth surface at an angle of 90° to the fourth surfacethen there will be an angle of 60° between a laser beam which isincident on the fourth surface of the block and the laser beam which isemitted from fifth surface of the block. In this case, to achieve theangle of 60° between a laser beam which is incident on the fourthsurface of the block and light which is emitted from fourth surface ofthe block, the block could preferably be arranged relative to the lasersource so that the laser beam emitted from the laser source is incidenton the fourth surface of the block at an angle of 90°; however it willbe understood that the block could be configured to provide the angle of60° between the incident and emitted a laser beams for any particularangle of incident on the fourth surface of the block.

Likewise, the block may be configured so that there is an angle of 45°between the first and second surfaces, and an angle of 90° between thefourth and fifth surfaces, so that there is an angle of 90° between alaser beam which is incident on the third surface of the block and thelaser beams which are emitted from the fifth surface of the block. Inthis case, to achieve the angle of 90° between a laser beam which isincident on the fourth surface of the block and the laser beams whichare emitted from fifth surface of the block, the block should bearranged relative to the laser source so that the laser beam emittedfrom the laser source is incident on the fourth surface of the block atan angle of 90°; however it will be understood that the block could beconfigured to provide the angle of 90° between the incident and emittedlight beams for any particular angle of incident on the fourth surfaceof the block.

Likewise, the block may be configured so that there is an angle of 65°between the first and second surfaces, and an angle of 130° between thefourth and fifth surfaces, so that there is an angle of 50° between alaser beam which is incident on the fourth surface of the block and alaser beam which is emitted from fifth surface of the block. In thiscase, to achieve the angle of 65° between a laser beam which is incidenton the fourth surface of the block and light which is emitted from fifthsurface of the block, the block should be arranged relative to the lasersource so that the laser beam emitted from the laser source is incidenton the fourth surface of the block at an angle of 90°; however it willbe understood that the block could be configured to provide the angle of50° between the incident and emitted light beams for any particularangle of incident on the fourth surface of the block.

Preferable the angles between the first and second surfaces is given by180=2α+β+Ω where β is the angle defined between the input light andreflected light on the first reflective surface, Ω is the angle definedbetween the first reflected light and the reflected light on the secondreflective surface and α is the input angle of the light beam to theblock according to the normal.

At the manufacturing stage the first part of the block may be shaped sothat the desired angles between the first and second surfaces areachieved. At the manufacturing stage the second part of the block may beshaped so that the desired angles between fourth and fifth surfaces areachieved.

The means for beam splitting may comprise dielectrical or hybriddielectrical material.

The means for beam splitting may be configured to split the laser beamemitted by the laser to provide a first laser beam portion which has afirst intensity and a second laser beam portion which has a secondintensity. The means for beam splitting may be configured to be anon-polarizing beam splitter. The non-polarizing beam splitter may be acoating. As previously indicated, the non-polarizing beam splitter ispreferably provided in the form of a coating provided on the thirdsurface of the first part of the block. The non-polarizing beam splitteris preferably hybrid dielectric coating. The non-polarizing beamsplitter may comprise a combination of metal (aluminium, silver or evengold) coating and/or dielectric coating (magnesium fluoride, calciumfluoride, and various metal oxides).

The means for beam splitting may be configured to split the laser beamemitted by the laser to provide a first laser beam portion which has afirst polarization and a second laser beam portion which has a secondpolarization, wherein the first and second polarisations are orthogonal.The means for beam splitting may be configured to be a polarizing beamsplitter. The polarizing beam splitter may be a coating. As previouslyindicated, the polarizing beam splitter is preferably provided in theform of a coating provided on the third surface of the first part of theblock. The polarizing beam splitter may comprise dielectric; preferablythe polarizing beam splitter is pure dielectric. The polarizing beamsplitter preferably comprises layers of materials such as magnesiumfluoride, calcium fluoride and various metal oxides.

The means for beam splitting may comprise at least one material selectedfrom the group comprising Al, Au, Ag, SiO₂, TiO₂, Al₂O₃, Ta₂O₅, MgF₂,LaF₃ and AlF₃. Alternatively means for beam splitting may comprise anyof those metals with alloys.

According to a further aspect of the present invention there is provideda projection device comprising, one or more light assemblies accordingto any one of the above-mentioned light assemblies, and one or more MEMSmirrors which can oscillate about at least one oscillation axis to scanlight which has been emitted from the one or more light assemblies,across a projection screen to project an image on the projection screen.

The one or more light assemblies my each comprise at least three lasersources.

The block of a light assembly may be arranged relative to the at leastone laser source, such that laser beams are emitted from the block in adirection which ensures that there is a angle, other than 0° or 180° or360°, between a laser beam emitted from the at least one laser sourceand is incident on the block and a laser beam emitted from the block tothe MEMS mirror.

The block of a light assembly may be arranged relative to a MEMS mirror,such that laser beams which are emitted from the block are incident on asurface of the MEMS mirror at an angle to the surface of the MEMS mirrorwhich is always greater than half of the angle of oscillation of theMEMS mirror, as the MEMS mirror undergoes full oscillation. Preferablythe block of a light assembly is arranged relative to a MEMS mirror,such that laser beams which are emitted from the block are incident on asurface of the MEMS mirror at an angle to the surface of the MEMS mirrorwhich is just above half of the total optical angle of oscillation ofthe MEMS mirror, as the MEMS mirror undergoes full oscillation.Preferably the block of a light assembly is arranged relative to a MEMSmirror, such that laser beams which are emitted from the block areincident on a surface of the MEMS mirror at an angle to the surface ofthe MEMS mirror which is between 0.1°-45° greater than, and mostpreferably between 1°-10°, greater than, half of the total optical angleof oscillation of the MEMS mirror, as the MEMS mirror undergoes fulloscillation. The optical angle is preferably twice the mechanicaloscillation angle of the MEMS mirror.

In any of the above mentioned projection devices a light assembly maycomprise three laser sources and the component for reducing speckle ofthe light assembly may be arranged to receive laser beams from the threelaser sources.

The projection device may comprise at least two further laser sources inaddition to the laser sources provided in the one or more lightassemblies. For example the light assembly may comprise a laser sourcewhich provides a red laser beam, and the projection device may comprisea further two laser sources which are configured to provide a blue andgreen laser beam respectively. The light assembly in this particularexample will emit a red laser beam. However, it will be understood thatthe light assembly may comprise a laser source which is configured toemit any colour laser beam e.g. blue or green, and/or an Infra-red lightand/or UV light. Likewise the two laser sources of the project devicemay be configured to emit any colour laser beam and/or an Infra-redlight and/or UV light. The light beams from each laser source may becombined to define a pixel.

The projection device may further comprise a beam combiner which isconfigured to combine the laser beams emitted from the one or more lightassemblies with the light beams emitted by the at least two furtherlaser sources which are provided in the projection device.

A light assembly in the projection device may further comprise a beamcombiner.

A light assembly of the projection device may comprise three lasersources. The component for reducing speckle in a light assembly of theprojection device may be arranged to receive laser beams from the threelaser sources. The three laser sources may comprise a red, green andblue laser source.

The projection device may comprise at least one other component forreducing speckle, in addition to the component(s) for reducing specklewhich is/are provided in the one or more assemblies. For example, theprojection device may comprise a single light assembly which comprises afirst component for reducing speckle, and the projection device maycomprise a second component for reducing speckle. The at least one othercomponent for reducing speckle may have some or all of the features ofthe afore-mentioned components for reducing speckle.

The least one other component for reducing speckle may be configured tocomprise a non-polarizing beam splitter if the component for reducingspeckle in the one or more light assemblies is configured to comprise anon-polarizing beam splitter. The second component for reducing specklemaybe configured to comprise a non-polarizing beam splitter means if thecomponent for reducing speckle in the one or more light assemblies isconfigured to comprise a polarizing beam splitter.

The least one other component for reducing speckle may be configured tooutput a laser beam to one or more MEMS mirrors which can oscillateabout at least one oscillation axis to scan light across a projectionscreen.

Preferably the least one other component for reducing speckle isarranged such that the one or more MEMS mirrors of the projection deviceare offset from a central axis of the least one other component forreducing speckle may be configured. Preferably least one other componentfor reducing speckle may be configured comprises a block having some orall of the features of the afore-mentioned blocks, and the block isarranged such that the one or more MEMS mirrors are offset from acentral axis of the block.

Preferably the at least one other component for reducing speckle isconfigured to receive a laser beam output from a light assembly in theprojection device and laser beams output from the two further lasersources provided in the projection device.

The at least one other component for reducing speckle is preferablyconfigured to receive a combined laser beam, wherein the combined laserbeam comprises a laser beam output from the light assembly and laserbeams output from the two further laser sources.

The projection device may comprise a plurality of other components forreducing speckle, in addition the component(s) for reducing speckleprovided in the one or more light assemblies. For example a second,third and more components for reducing speckle may be provided in theprojection device. The plurality of other components for reducingspeckle may be arranged in a stack. This will result in a greaterreduction in speckle. Preferably one component in the stack comprises apolarizing coating and all the other components in the stack comprisenon-polarizing coating. Preferably the second components for reducingspeckle will comprise a polarising beam splitter and the third and aboveadditional components for reducing speckle will preferably comprise anon-polarizing beam splitter.

In the projection device the block may be arranged such that laser beamswhich are emitted from the fifth surface of the block, are emitted in adirection which ensures that they are always incident on the surface ofthe MEMS mirror at an angle to the surface of the MEMS mirror which isalways greater than half of the total optical scanning angle ofoscillation of the MEMS mirror. If the angle to the surface of the MEMSmirror was less than the angle of oscillation of the MEMS mirror thenthe projected image would be distorted. Advantageously the angle atwhich the light beams are incident on the surface of the MEMS mirror canbe adjusted by configuring the block to have at least its first andsecond surfaces at appropriate orientations. The block is designed suchthat it fits the input versus output angle of the laser beam, the outputangle enabling to reach the MEMS mirror with an angle just above thehalf of its total optical scanning angle. Also the angle at which thelight beams are incident on the surface of the MEMS mirror could beadjusted by moving the block; however to decrease the angle of incidenceof the laser beam on the MEMS mirror would require that the block bemoved further from the MEMS mirror, thus requiring a larger package orhousing for the projection device.

The block could be used to direct laser beams which it emits to a MEMSmirror. There may be further provided a method for modifying an existingprojection system or projection device, comprising the step of replacinga reflecting means which is used to deflect light emitted from a beamcombiner to a MEMS mirror, with a block which has one or more of theabove mentioned features. In this way the block could be used to alignlight beams with the MEMS mirror.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood with the aid of the descriptionof an embodiment given by way of example only and illustrated by thefigures, in which:

FIG. 1 shows a side view of a light assembly according to a first aspectof the present invention;

FIG. 2 shows a side view of a light assembly according to a secondaspect of the present invention;

FIG. 3a &b shows variations of the blocks which are used in the lightassemblies of FIG. 1 and FIG. 2;

FIG. 4 shows a schematic representation of a projection device accordingto a further aspect of the present invention;

FIG. 5 shows a schematic representation of a projection device accordingto a further embodiment of the present invention;

FIG. 6 shows a schematic representation of a projection device accordingto a further embodiment of the present invention;

FIG. 7 shows a side view of a light assembly according to a furtheraspect of the present invention;

FIG. 8 shows a side view of a light assembly according to a furtheraspect of the present invention.

DETAILED DESCRIPTION OF POSSIBLE EMBODIMENTS OF THE INVENTION

FIG. 1 shows a side view of a light assembly 1 according to a firstaspect of the present invention. The light assembly 1, comprises, alaser source 3 which is operable to emit a laser beam 5, and a componentfor reducing speckle 7. The component for reducing speckle 7 is arrangedto receive the laser beam 5 from the laser source 3.

The component for reducing speckle 7 comprises a block 21 which is madeup of a first part 50, and a second part 51. The first and second parts50,51 are each configured to have a triangular cross section(alternatively the first and/or second parts 50,51 may comprise atruncated-triangular cross section). The first part 50 comprises threesurfaces which define a first 23, second 25 and third 26 surface of theblock 21, while the second part 51 comprises three surfaces which definea fourth 27, fifth 29 and sixth 30 surface of the block 21. it will beunderstood that the second part 51 is an optional feature and theinvention can still be carried out when the block comprises a first part50 only.

The component for reducing speckle 7 comprises, a means for beamsplitting 9. In this particular example the means for beam splitting 9is defined by a coating 43 which is provided on the third surface 26 ofthe first part 50 of the block 21. Alternatively the means for beamsplitting 9 could be a coating provided on the sixth surface 30 of thesecond part 51. The coating 43 may comprise dielectric materials such asAl, Au, Ag, SiO₂, TiO₂, Al₂O₃, Ta₂O₃, MgF₂, LaF₃ and/or AlF₃ such thatthe means for beam splitting 9 is configured to be a polarizing beamsplitter.

The means for beam splitting 9 is configured to split the laser beam 5emitted by the laser 3, by reflecting a first portion 11 of the laserbeam 5 and transmitting a second portion 13 of the laser beam 5. In thisparticular example the means for beam splitting 9 is configured to be apolarizing beam splitter; that is, the means for beam splitting 9 isconfigured to split the laser beam 5 emitted by the laser 3 to provide afirst laser beam portion 11 which has a first polarization and a secondlaser beam portion 13 which has a second polarization, wherein the firstand second polarisations are orthogonal to one another. Therefore thecoating 43 on the third surface 26 of the first part 50 which definesthe component for reducing speckle 7 comprises a dielectric materialsuch as, for example, Al, Au, Ag, SiO₂, TiO₂, Al₂O₃, Ta₂O₅, MgF₂, LaF₃and/or AlF₃.

It will be understood that the means for beam splitting is not limitedto being a polarizing beam splitter e.g. the means for beam splittingcould be a non-polarizing beam splitter. (Of course if the means forbeam splitting is non-polarizing, then the beams would be split intobeams of different intensities and not into beams of differentpolarisations).

The component for reducing speckle 7 comprises at least a first andsecond reflective means 15,17. The first reflective means 15 is arrangedto receive the second portion 13 of the laser beam 5 from the means forbeam splitting 9. The first and second reflective means 15,17 arearranged such that the second portion 13 of the laser beam 5 can bedirected from the first reflective means 15 to the second reflectivemeans 17. The second reflective means 17 is arranged such that it candirect the second portion 13 of the laser beam 5 back to the means forbeam splitting 9. This means that the first reflective means 15, locatedon the first surface 23, can receive light beams from the means for beamsplitting 9 and the second reflective means 17, located on the secondsurface 25, can reflect laser beams it received from the firstreflective means 15 back to the means for beam splitting 9. In thisparticular example the first reflective means 15 and the secondreflective means 17 are defined by reflective coatings 31,33 which areprovided on the first and second surfaces of the first part 50 of theblock 21 respectively. The first and second reflective means 15,17 andmeans for beam splitting 9 are arranged to define an optical path 19.The first and second reflective means 15,17 and means for beam splitting9 are arranged such that the length of optical path 19 is greater than acoherence length of the laser beam 5 which is emitted from the lasersource 3. Since the first and second reflective means 15,17 and meansfor beam splitting 9 are provided on the first, second and thirdsurfaces 23,25,26 respectively, the arrangement of these components toprovide an optical path 19 which is greater than a coherence length ofthe laser beam 5, can be achieved by configuring the first part 50 ofthe block 21 to have the appropriate dimensions e.g. to increase thelength of the path 19 a large size first part 50 could be provided.

The first 23, second 25, fourth 27 and fifth 29 surface, of the block 21are each in optical communication with the means for beam splitting 9(which is defined by a coating on the third surface of the block). Thethird 26 and sixth 30 surfaces are also in optical communication withthe means for beam splitting 9. The fourth surface 27 of the block 21 isconfigured to receive the laser beam 5 emitted by the laser source 3 andallow the received laser beam to pass to the means for beam splitting 9.The fifth surface 29 of the block 21 is configured to emit from theblock 21 both the first portion 11 of the laser beam 5 which isreflected by the means for beam splitting 9 and at least a part 41 ofthe second portion 13 of the laser beam 5 which has been transmittedthrough the means for beam splitting 9, to the first and secondreflective means 15,17 and back through the means for beam splitting 9.Each of the fourth 27 and fifth 29 surfaces comprise an anti-reflectivecoating 35,37.

The first and second surfaces 23,25 are orientated such that the firstportion 11 of the laser beam 5 and said at least a part 41 of the secondportion 13 of the laser beam 5, can be emitted in parallel in the samedirection from the fifth surface 29 of the block 21. This is because theorientation of the first and second surfaces 23,25 will determine theangle at which the first and second reflective means reflect the lightbeams they receive. It will be understood that the orientation of thefourth and fifth surface could also be utilized to influence thedirection in which light is emitted from the block 21; therefore thefirst, second, fourth and fifth surfaces 23,25,27,29 may be orientatedsuch that the first portion 11 of the laser beam 5 and said at least apart 41 of the second portion 13 of the laser beam 5, can be emitted inparallel in the same direction from the fifth surface 29 of the block21.

In this particular example the first, second, fourth and fifth surfaces23,25,27,29 are orientated such that the first portion 11 of the laserbeam 5 and said at least a part 41 of the second portion 13 of the laserbeam 5, form a predefined angle with the light beam 5 which is incidenton the fourth surface 27 of the block 21. For example, in the particularexample shown in FIG. 1, the block 21 is shaped so that there is anangle of 60° between the first and second surfaces 23,25, and an angleof 120° between the fourth and fifth surfaces 27,29; as a result,provided that the laser beam 5 from the laser source 3 is incident onthe fourth surface 27 at an angle of 90° to the fourth surface 27, thenthere will be an angle of 60° between the laser beam 5 which is incidenton the fourth surface 27 and laser beams 11,41 which are emitted fromfifth surface 29 of the block 21. In this case, to achieve the angle δof 60° between the laser beam 5 which is incident on the fourth surface27 of the block 21 and the laser beams 11,41 which are emitted fromfifth surface 29 of the block 21, the block 21 should be arrangedrelative to the laser source 3 so that the laser beam 5 emitted from thelaser source 3 is incident on the fourth surface 27 of the block 21 atan angle of 90°. However it will be understood that the block 21 couldbe configured to provide the angle of 60° between the incident andemitted laser beams for any particular angle of incident on the fourthsurface 27 of the block 21. Preferably the block 21 is shaped at themanufacturing stage so that the desired angles between the surfaces23,25,27,29 are provided. It should be understood that a predefinedangle between the light beam 5 which is incident on the fourth surface27 of the block 21 and the light beams 11,41 which are emitted from theblock 21 could be achieved by orientating the first and second surfaces23,25 only in an appropriate orientation.

The first part 50 and second part 51 are arranged such that the sixthsurface 30 of the block 21 (provided by a surface of the second part 51)abuts the coating 43 provided on the third surface 26 of the first part50. In this manner the first part 50, second part 51 and means for beamsplitting 9, form a single unit. The first part and second parts 50,51may be secured together in their abutted position.

The block 21 may be configured such that the first and/or second parts50,51 are changeable with other first and/or second parts 50,51 whichhave different dimensions e.g. different angles between the first andsecond surfaces 23,25, and/or between the fourth and fifth surfaces27,29. A user can thus, for example, select to use first and secondparts 50,51 which have the appropriate orientated surfaces which providea desired angle between the laser beams which are incident to the block21 and the laser beams emitted 11,41 from the block 21.

During use the laser source 3 is operated to emit a laser beam 5. Theblock 21 is orientated so that the laser beam 5 is incident on thefourth surface 27 of the block. In particular, for this example, theblock 21 is orientated so that the laser beam 5 is incident at 90° tofourth surface 27 of the block 21.

The light beam 5 passes through the fourth surface 27, into the block21, and onto the means for beam splitting 9 (i.e. coating 43 provided onthe third surface of the first part 50). The means for beam splitting 9splits the light beam 5 into a first laser beam portion 11 which has afirst polarization and a second laser beam portion 13 which has a secondpolarization, wherein the first and second polarisations are orthogonalto one another.

The first laser beam portion 11 is reflected by the means for beamsplitting 9 to the fifth surface 29 of the block 21. The first laserbeam portion 11 is subsequently emitted from the block 21 through thefifth surface 29.

The second laser beam portion 13 which is transmitted through the meansfor beam splitting 9 (i.e. emitted beam 41), will be emitted from theblock 21 through the fifth surface 29. The emitted beam 41 will beemitted the fifth surface 29, in the same direction as the first laserbeam portion 11. Since the second laser beam portion 13 will have passedalong the optical path 19, and since the optical path 19 has a lengthwhich is greater than the coherence length of the laser beam 5, theemitted beam 41 will be delayed with respect to the first laser beamportion 11. As a result, there will be difference between the phase ofthe emitted beam 41 and first laser beam portion 11, when they areemitted from the fifth surface 29 of the block 21; this will result in areduction in speckle. Notably, unlike the devices used in the prior art,no quarter-wave plates are required to achieve a reduction in specklebecause no polarization change is required here to split the laser beamand recombine them in the same direction. Simple reflection only is usedto recollimate the beams, that were initially split using the polarizedbeam splitter, together

FIG. 2 shows a side view of a light assembly 100 according to a secondaspect of the present invention. The light assembly 100 shown in FIG. 2has many of the same features as the light assembly 1 shown in FIG. 1and like features are awarded the same reference numbers.

In the light assembly 100 comprises a means for beam splitting 109 whichis configured to be a non-polarizing beam splitter; that is the meansfor beam splitting 109 is configured to split the laser beam 5 emittedby the laser 5 to provide a first laser beam portion 111 which has afirst intensity and a second laser beam portion 113 which has a secondintensity. As was the case for the assembly shown in FIG. 1, the firstlaser beam portion 111 is reflected by the means for beam splitting 109and the second laser beam portion 113 is transmitted through the meansfor beam splitting 109 to be passed along the optical path 19. When thesecond laser beam portion 113 is passed back to the means for beamsplitting 109, it will be split again with part 141 of the second laserbeam portion 113 which has a first intensity being transmitted throughthe means for beam splitting 109 and the other part 151 of the secondlaser beam portion 113 which has another intensity being passed backalong the optical path 19. When the laser beam portion 151 goes into theoptical loop 19, it will split again with part 161 of the laser beamportion 151 which has one intensity being transmitted through the meansfor beam splitting 109 and the another part 171 of the laser beamportion 151 which has another intensity being passed back along theoptical path 19. Continuous looping of the light beam will occur withpart of the beam being transmitted through the means for beam splittingand another part of the beam being passed back into the optical loop 19once again. All of the light beams 141,161 which are emitted from themeans for beam splitting 109 will each be emitted in the same directionand/or parallel from the fourth surface 29 of the block 21. There willbe an infinite number of light beams 141,161,111 output from the fourthsurface 29 of the block 21 this is due to the infinite looping of lightbeams in optical loop 19. The light beams 141,161,111 output from thefourth surface 29 of the block 21 will be collimated together. This isprimarily due to the means for beam splitting 109 which is configured tobe a non-polarizing beam splitter.

As was the case for the assembly shown in FIG. 1, the means for beamsplitting 109 is defined by a coating 143 which is provided on the thirdsurface 26 of the first part 50 of the block 21. The coating 143 maycomprise a hybrid dielectric material so that the means for beamsplitting 109 is configured to be a non-polarizing beam splitter. Thenon-polarizing beam splitter may comprise a combination of metal(aluminium, silver or even gold) coating and/or dielectric coating(magnesium fluoride, calcium fluoride, and various metal oxides).

The light assembly 100 shown in FIG. 2 operates in the same manner asthe assembly 1 of FIG. 1, and offers the same advantages; except thatthe means for beam splitting 109 splits laser beams into laser beams ofdifferent intensities rather than into laser beams which have differentpolarizations. The light assembly 100 offers the additional advantage inthat non-polarising beam splitters are cheaper than polarising beamsplitters, thus the light assembly 100 is cheaper to manufacturecompared to light assembly 1 shown in FIG. 1. The assembly of FIG. 1shows two output beams recollimated with an optical path differencelonger than the coherence length of the laser beam, achieving a specklereduction of at most 30% if the two polarization components are of samequantities. By controlling the ratio between the two polarization, thelight intensity between the two output beams can be controlled. By doingso, there will be less speckle reduction but more control over theamount of reduced speckle. The assembly 100 shown in FIG. 2 shows atheoretical output of an infinity of laser beams each with an additionaloptical path difference longer than the coherence length of the lasersource. So speckle reduction will be more important as there is moreuncorrelated speckle as an output in comparison with the assembly ofFIG. 2. Furthermore, according to the means for beam splitting 109 i.e.the ratio of light intensity split given, the intensity between theoutput beams can be controlled and thus the amount of reduced specklecan be reduced as well (up to 43%).

In each of the embodiments previously described the first, second,fourth and fifth surfaces 23,25,27,29 are arranged so that angle of 60°exists between the laser beam 5 incident on the fourth surface 27 of theblock 21 and the laser beams 11,41,111,141,171 emitted from the fifthsurface 29 of the block 21. However, it will be understood that thefirst, second, fourth and fifth surfaces 23,25,27,29, may be orientatedat any angle to achieve any desired angle between laser beams incidentto and emitted from the block 21. FIGS. 3a and 3b show blocks 80,90which has first, second, fourth and fifth surfaces 23,25,27,29,orientated at different angles to achieve a different angle α, ρ betweenincident light beams 5 and emitted light beams 11,41. The blocks 80,90may comprise some or all of the features of the block 21 used in thelight assemblies 1,100 shown in FIGS. 1 and 2 respectively.

FIG. 3a shows a block 80 which is configured so that there is an angle‘w’ of 65° between the first and second surfaces 23,25, and an angle ‘t’of 130° between the fourth and fifth surfaces 27,29, so that an angle‘a’ of 50° between the laser beam 5 which is incident on the fourthsurface 27 and the laser beams 41,11 which are emitted from fifth 29surface of the block 21.

FIG. 3b shown that the block may be configured so that there is an angle‘x’ of 45° between the first and second surfaces 23,25, and an angle of90° between the fourth and fifth surfaces 27,29, so that there is anangle of 90° between the laser beam 5 which is incident on the fourthsurface 27 of the block 90 and the laser beams 11,41 which are emittedfrom the fifth surface 29 of the block 90. It is also worth noting thatthe first part 50 of the block 90 is configured to have atruncated-triangular cross section.

FIG. 4 shows a schematic representation of a projection device 200according to a further aspect of the present invention. The projectiondevice 200 comprises a light assembly 1 as shown in FIG. 1. It will beunderstood that the projection device 200 may additionally oralternatively comprise a light assembly 100 as shown in FIG. 2. Theprojection device 200 further comprises a MEMS mirror 201 which canoscillate about two orthogonal oscillation axes 203,205 to scan light403 which it receives.

The projection device 200 has two further laser sources 211,213 whichare configured to provide green and blue laser beams 217,219respectively. The light assembly 1 in this particular example comprisesa laser source 3 which is configured to emit a red laser beam 5.However, it will be understood that the light assembly 1 may comprise alaser source which is configured to emit any colour laser beam e.g blueor green. Likewise the two laser sources of the project device may beconfigured to emit any colour laser beam and/or an Infra red laser beamand/or a UV laser beam.

The projection device 200 further comprises a beam combiner 223 which isconfigured to combine the red laser beams 211 emitted from the lightassembly 1 with the green and blue laser beams 217,219 emitted by thetwo further laser sources 211,213 to provide a combined light beam 220.The light beams 211,217,219 are combined to define pixels of an imagewhich is to be projected. The beam combiner 223 in this particularexample comprises a green dichroic plate and blue dichroic plate225,227.

The combined light beam 220 which is output from the beam combiner 223is directed, via an intermediate mirror 230 to the MEMS mirror 201. TheMEMS mirror 201 is operated to oscillate about its two orthogonaloscillation axes 203,205 to scan combined light beam 220 across thedisplay screen 209 to project pixels which define the image 221.

FIG. 5 shows a schematic representation of a projection device 400according to a further embodiment of the present invention. Theprojection device 400 has many of the same features as the projectiondevice 200 shown in FIG. 4 and like features are awarded the samereference numbers.

The projection device 400 comprises a second component for reducingspeckle 401 in the form of a second block 401. The second block 401 mayhave some or all of the features of the blocks 21,80,90 discussedearlier. Preferably the means for beam splitting 9,109 in the secondblock is different to that provided in the block 21 of the lightassembly 1. In this particular example, since the light assembly 1comprise a block 21 which comprises a polarising beam splitter, thesecond block 401 is configured to comprise a non-polarizing beamsplitter. It will be understood that if the light assembly was a lightassembly 100 according to that shown in FIG. 2 (i.e. having anon-polarizing beam splitter), then the second block 401 wouldpreferably be configured to comprise a non-polarizing beam splitter.

The second block 401 is arranged to receive the combined laser beam 220output from beam combiner 223 and to output laser beams 403 to the MEMSmirror 201 which can oscillate about it two orthogonal oscillation axis203,205 to scan the laser beam across a projection screen 209 so that animage 221 is projected.

The second block 401 is arranged such that it is are offset from theMEMS mirror 201 so as to ensure that the second block 401 does notobstruct light beams which are reflected by the MEMS mirror 201 to thedisplay screen 209. Preferably the second block 401 is arranged so thatthe MEMS mirror 201 is offset from a central axis of the block 401.

The second block 401 is further arranged such that laser beams 403 whichare emitted from the fifth surface 29 of the second block 401, areemitted in a direction which ensures that there is a angle other than 0°or 90° or 180° between the combined laser beam 220 incident on the thirdsurface 27 of the second block 401 and laser beams 403 which are emittedfrom the fifth surface 29 of the second block 401.

Additionally the block 401 of a light assembly is arranged relative to aMEMS mirror 201, such that laser beams which are emitted from the block401 are incident on a surface of the MEMS mirror at an angle to thesurface of the MEMS mirror which is always greater than half of theangle of oscillation of the MEMS mirror, as the MEMS mirror undergoesfull oscillation.

FIG. 6 shows a schematic representation of a projection device 300according to a further embodiment of the present invention. Theprojection device 300 comprises a light assembly 301 which is similar tothat shown in FIG. 1 except that three laser sources 305,307,309 areprovided in the light assembly 301. The three laser sources 305,307,309are configured to provide a red, green and blue laser beams 311,313,315respectively. The light assembly 301 further comprises a beam combiner333 which is configured to combine red, green and blue laser beams311,313,315 to provide a combined laser beam 323; the combined laserbeam 323 is passed to the block 21.

The laser beams emitted from the block 21 are directed to the a MEMSmirror 201 which can oscillate about two orthogonal oscillation axis203,205 to scan light which has been emitted from the light assembly301, across a projection screen 209.

In this particular example the block 21 is arranged such that laserbeams which are emitted from the fifth surface 29 of the block, areemitted in a direction which ensures that they are always incident onthe surface of the MEMS mirror 201 at an angle β to the surface of theMEMS mirror 201 which is always greater than half of the angle ofoscillation of the MEMS mirror 201, as the MEMS mirror 201 undergoesoscillation. If the angle β to the surface of the MEMS mirror 201 wasless than the angle of oscillation of the MEMS mirror 201 then theprojected image would be distorted. Advantageously the angle at whichthe light beams are incident on the surface of the MEMS mirror 201 canbe adjusted by configuring the block 21 to have at least its first andsecond 23,25 (and optionally it third 26 and fourth 30 surfaces) to havethe appropriate orientations. The angle at which the light beams areincident on the surface of the MEMS mirror 201 could be adjusted bymoving the block 21 however to decrease the angle of incidence wouldrequire that the block 21 be moved further from the MEMS mirror 201,thus requiring a larger package or housing for the projection device300.

The block 21 is positioned at a angle other than 90° between thecombined laser beam 323 incident on the third surface 27 of the block 21and light beams emitted from the fourth surface 29 of the block 21. Thiswill reduce distortion in a projected image.

FIG. 7 shows a light assembly 700 according to a further embodiment ofthe present invention. The light assembly has many of the same featuresof the light assembly 1 shown in FIG. 1 and like features are awardedthe same reference numbers.

Unlike the light assembly 1 shown in FIG. 1 light assembly 700 comprisesblock 721 which consists of the first part 50 only. The surfaces of thefirst part 50 defines the first, second and third surfaces surfaces23,25,26; the first part 50. Light beams 5 are incident on the block 21and light beams 41,11 are emitted from the block 721 through the thirdsurface 26.

The means for beam splitting 9 is configured to be a coating 43 providedon the third surface 26 of the first part 50. The coating 43 maycomprise dielectric Al, Au, Ag, SiO₂, TiO₂, Al₂O₃, Ta₂O₅, MgF₂, LaF₃and/or AlF₃ (common dielectric materials) such that the means for beamsplitting 9 is configured to be a polarizing beam splitter.Alternatively the coating 43 may be configured to be a non-polarizingbeam splitter.

As was the case of the light assembly 1 shown in FIG. 1, in the lightassembly 700 the angle between the laser beam 5 which is incident on theblock 721 and the laser beams 41,11 which are emitted from the block 721is dictated by the orientations of the first and second reflective means31,33 which is dictated by the orientation of the first and secondsurfaces 23,25 since the first and second reflective means 31,33 aredefined by coatings on the first and second surfaces 23,25.

The light assembly 700 operates in a similar fashion the light assembly1 shown in FIG. 1.

FIG. 8 provides a side view of a light assembly 880, according to thepresent invention. The light assembly 880 comprises a laser source 3which is operable to emit a laser beam 5, and a component for reducingspeckle 881. The component 881 for reducing speckle is arranged toreceive the laser beam 5.

In this particular embodiment the component 881 for reducing speckle isdefined by three discrete elements, namely, a first and second mirror883,884 (which define a first and second reflective means respectively),and a beam splitter plate 885 (which defines a means for beamsplitting). The beam splitter plate 885 may be configured to be apolarising beam splitter or a non-polarising beam splitter. Furthermorethe beam splitter plate 885 could be defined by a coating provided on anoptical component. It will be understood that the beam splitter plate885 may be momochromatic or may be polychromatic. It will also beunderstood that the beam splitter plate 885 could be configured to haveany suitable shape, for example it could be configured to have atriangular cross section; preferably the beam splitter plate 885 will beconfigured to be a planar structure. Preferably, if the the beamsplitter plate 885 is configured to be momochromatic, then it will be aplanar structure; if the beam splitter plate 885 is configured to bepolychromatic then it will have a triangular cross section. A beamsplitter plate 885 which is configured to be polychromatic can outputcollimated beams independently of the wavelengths of the light which areincident on the beam splitter plate 885. Each of the first mirror 883,second mirror 884 and beam splitter plate 885 are mechanicallyindependent of one another such that they can each be moved andpositioned independently of the one another.

A beam splitter plate 885 is configured to split the laser beam 5emitted by the laser 3, by reflecting a first portion 13 of the laserbeam and transmitting a second portion 11 of the laser beam.

The first mirrors 883 is arranged to receive the second portion 13 ofthe laser beam from the beam splitter plate 885 and the second mirror884 is arranged such that it can direct the second portion 13 of thelaser beam back to the beam splitter plate 885. The first and secondmirrors 883,884 are arranged such that the second portion 13 of thelaser beam can be directed from the first mirrors 883 to the secondmirror 884. The first and second mirror 883,884 and beam splitter plate885 are arranged to define an optical path 19 for the second portion 13of the laser beam whose length is equal to, or greater than, a coherencelength of the laser beam 5 which is emitted from the at least one lasersource 3.

The optical assembly 880 operates in a similar fashion to the opticalassembly 1 shown in FIG. 1.

Various modifications and variations to the described embodiments of theinvention will be apparent to those skilled in the art without departingfrom the scope of the invention as defined in the appended claims.Although the invention has been described in connection with specificpreferred embodiments, it should be understood that the invention asclaimed should not be unduly limited to such specific embodiment.

1-15. (canceled)
 16. An apparatus to reduce speckle, comprising: a firstpart comprising a first surface, a second surface, and a third surface,the first surface, the second surface, and the third surface arranged inoptical communication with each other; a second part comprising a fourthsurface, a fifth surface, and a sixth surface, the sixth surface inoptical communication with the fourth and fifth surfaces; and a beamsplitting plate disposed between the third surface and the sixthsurface, the beam splitting plate to split an incident laser beam byreflecting a first portion of the laser beam and transmitting a secondportion of the laser beam, the sixth surface to transmit the laser beamto the beam splitting plate and to transmit the second portion of thelaser beam to the fifth surface, the third surface to transmit thesecond portion of the laser beam to the first surface, the first surfaceto define a first mirror arranged to receive the second portion of thelaser beam from the beam splitting plate and reflect the second portionof the laser beam to the second surface; the second surface to define asecond mirror arranged to receive the second portion of the laser beamfrom the first mirror and to direct the second portion of the laser beamto the third surface, the first and the second mirrors and the thirdsurface arranged to define an optical path for the second portion of thelaser beam with a length equal to, or greater than, a coherence lengthof the laser beam, the fourth surface to receive the laser beam andcommunicate the laser beam to the sixth surface, and the fifth surfaceto receive the second portion of the laser beam from the sixth surfaceand to receive the first portion of the laser beam from the thirdsurface, an orientation between the first and second surface and betweenthe fourth and fifth surfaces such that the first portion of the laserbeam is transmitted through the fifth surface in parallel to the secondportion of the laser beam.
 17. The apparatus of claim 16, at least twoof the first mirror, the second mirror, and the beam splitting plate canbe moved independently of the one another.
 18. The apparatus of claim16, the third surface to comprise a coating to define the beam splittingplate.
 19. The apparatus of claim 16, the first surface and the secondsurface to comprise a coating to define the first and the secondmirrors, respectively.
 20. The apparatus of claim 16, wherein the firstpart and the second part are each configured to have a triangular crosssection, or a truncated-triangular cross section.
 21. A projectiondevice, comprising: a light assembly to emit light; and one or moremicroelectromechanical system (MEMS) mirrors to oscillate about at leastone oscillation axis to scan the light emitted from the light assemblyacross a projection screen to project an image on the projection screen,the light assembly comprising: at least one laser source operable toemit a laser beam; a first part comprising a first surface, a secondsurface, and a third surface, the first surface, the second surface, andthe third surface arranged in optical communication with each other; asecond part comprising a fourth surface, a fifth surface, and a sixthsurface, the sixth surface in optical communication with the fourth andfifth surfaces; and a beam splitting plate disposed between the thirdsurface and the sixth surface, the beam splitting plate to split anincident laser beam emitted by the laser source, by reflecting a firstportion of the laser beam and transmitting a second portion of the laserbeam, the sixth surface to transmit the laser beam to the beam splittingplate and to transmit the second portion of the laser beam to the fifthsurface, the third surface to transmit the second portion of the laserbeam to the first surface, the first surface to define a first mirrorarranged to receive the second portion of the laser beam from the beamsplitting plate and reflect the second portion of the laser beam to thesecond surface, the second surface to define a second mirror arranged toreceive the second portion of the laser beam from the first mirror andto direct the second portion of the laser beam to the third surface, thefirst and the second mirrors and the third surface arranged to define anoptical path for the second portion of the laser beam with a lengthequal to, or greater than, a coherence length of the laser beam, thefourth surface to receive the laser beam and communicate the laser beamto the sixth surface, and the fifth surface to receive the secondportion of the laser beam from the sixth surface and to receive thefirst portion of the laser beam from the third surface, an orientationbetween the first and second surface and between the fourth and fifthsurfaces such that the first portion of the laser beam is transmittedthrough the fifth surface in parallel to the second portion of the laserbeam.
 22. The projection device according to claim 21, the lightassembly comprising at least three laser sources.
 23. The projectiondevice according to claim 21, the light assembly positioned relative tothe one or more MEMS mirrors, such that laser beams emitted from thelight assemblies are incident on the surface of the MEMS mirror at anangle to the surface of the MEMS mirror which is always greater thanhalf of the total optical angle of oscillation of the MEMS mirror as theMEMS mirror undergoes full oscillation.
 24. The projection device ofclaim 21, comprising a plurality of light assemblies, the light assemblyas one of the plurality of light assemblies, each of the plurality oflight assemblies to comprise a light source, a beam splitter, a firstmirror, and a second mirror.
 25. A method comprising: receiving a lightbeam at a beam splitter, the beam splitter disposed between a first partand a second part, the first part comprising a first surface, a secondsurface, and a third surface, the second part comprising a fourthsurface, a fifth surface, and a sixth surface, the beam splitterdisposed between the third and sixth surfaces; splitting, at a beamsplitter, the light beam into a first light beam portion and a secondlight beam portion; reflecting, via the beam splitter, the first lightbeam portion to the fifth surface; transmitting, via the beam splitter,the second light beam portion to the first surface; reflecting, via atleast a first mirror at the first surface, the second light beam portionto the second surface; reflecting, via at least a second mirror at thesecond surface, the second light beam portion to the third surface, thefirst surface and the second surface to define an optical path, theoptical path to have a length equal to, or greater than, a coherencelength of the light beam; transmitting the second light beam portionthrough the third surface, the beam splitter and the sixth surface tothe fifth surface; and emitting, from the fifth surface, the first lightbeam portion and the second light beam portion.
 26. The method of claim25, comprising emitting the light beam from a laser light source. 27.The apparatus of claim 16, the beam splitting plate to split the laserbeam into the first part having a first polarization and the second parthaving a second polarization, the first polarization different from thesecond polarization.
 28. The apparatus of claim 16, the beam splittingplate to split the laser beam into the first part having a firstintensity and the second part having a second intensity, the firstintensity different from the second intensity.
 29. The apparatus ofclaim 19, the coating on the third surface comprising one or more of Al,Au, SiO₂, TiO₂, Al₂O₃, Ta₂O₅, MgF₂, LaF₃ or AIF₃.
 30. The apparatus ofclaim 16, wherein the first and second surfaces are arranged to form anangle of 60 degrees between them and the fourth and fifth surfaces arearranged to form an angle of 120 degrees between them.
 31. Theprojection device of claim 21, the third surface to comprise a coatingto define the beam splitting plate.
 32. The projection device of claim31, the beam splitting plate to split the laser beam into the first parthaving a first polarization and the second part having a secondpolarization, the first polarization different from the secondpolarization.
 33. The projection device of claim 32, the coating on thethird surface comprising one or more of Al, Au, SiO₂, TiO₂, Al₂O₃,Ta₂O₅, MgF₂, LaF₃ or AIF₃.
 34. The projection device of claim 21, thefirst surface and the second surface to comprise a coaling to define thefirst and the second mirrors, respectively.
 35. The projection device ofclaim 21, wherein the first part and the second part are each configuredto have a triangular cross section, or a truncated-triangular crosssection.
 36. The projection device of claim 35, wherein the first andsecond surfaces are arranged to form an angle of 60 degrees between themand the fourth and fifth surfaces are arranged to form an angle of 120degrees between them.
 37. The projection device of claim 21, the beamsplitting plate to split the laser beam into the first part having afirst intensity and the second part having a second intensity, the firstintensity different from the second intensity.
 38. The method of claim25, the third surface to comprise a coating to define the beam splitter.39. The method of claim 38, comprising splitting, via the beam splitter,the light beam into the first part having a first polarization and thesecond part having a second polarization, the first polarizationdifferent from the second polarization.
 40. The method of claim 39, thecoating on the third surface comprising one or more of Al, Au, SiO₂,TiO₂, Al₂O₃, Ta₂O₅, MgF₂, LaF₃ or AIF₃.
 41. The method of claim 25, thefirst surface and the second surface to comprise a coating to define thefirst and the second mirrors, respectively.
 42. The method of claim 25,wherein the first part and the second part are each configured to have atriangular cross section, or a truncated-triangular cross section. 43.The method of claim 42, wherein the first and second surfaces arearranged to form an angle of 60 degrees between them and the fourth andfifth surfaces are arranged to form an angle of 120 degrees betweenthem.
 44. The method of claim 25, comprising splitting, via the beamsplitter, the light beam into the first part having a first intensityand the second part having a second intensity, the first intensitydifferent from the second intensity.